Flashlight

The flashlight is a weapon in Doom 3. Its main purpose is to light up dark corridors in the original game, although it can be used as a club at close range. "UAC Standard issue light source. This model utilizes a static transfer power supply, so battery replacement is unnecessary."

- PDA description

Analysis
"Power fluctuations and maintenance issues continue to create poor lighting at the UAC Facility and flashlights are now required for all security forces. Also works as a club in close combat."

- Doom 3 instruction manual

With practice, the flashlight can be used to attack zombies to conserve ammo. Wraiths and cacodemons can also be defeated without taking damage if the player is careful, but attacking enemies other than that is not recommended. It has slightly shorter range than the fists when used in this way and has a lower "rate of fire" (i.e. a longer duration between each strike), but is about twice as powerful per hit. A useful tactic with the flashlight is to awaken dormant zombies, i.e. zombies which are laying on the ground where they might easily be mistaken for corpses. If it is a dormant zombie, it can be alerted to your presence by shining the flashlight at it from a distance, and can then be dealt with safely (it may require a moment of "wiggling" the flashlight beam to get the zombie's attention). In deathmatch, using the flashlight alerts other people to your whereabouts. The weapon is not included in the Xbox version's deathmatches.

When the player activates the Artifact's Berserk power in Resurrection of Evil, or collects the berserker powerup in Comm Transfer, the player receives a large boost to the damage output of their melee attacks which applies to the flashlight as well, to the point where a single swing can kill a Hell knight, mancubus or bruiser. It is not really any better or worse than the fists in this case, but it does at least continue to provide light while the player is berserk.

Trivia

 * The marine's inability to attach his flashlight to a weapon in the game, commonly known as "There's no duct-tape on Mars" problem, is often a subject of parody. This led to creation of the Duct Tape mod and its various successors. The aforementioned BFG Edition of Doom 3 and its later releases incorporated the armor-mounted flashlight by default.